Mabel, Heir to Cragflame is a rare Legendary Creature — Mouse Soldier card from Bloomburrow Promos (PBLB), collector number 224p. Current market price: $0.46 (foil $0.91), TCGplayer market prices via Scryfall.
Other Mice you control get +1/+1. When Mabel enters, create Cragflame, a legendary colorless Equipment artifact token with "Equipped creature gets +1/+1 and has vigilance, trample, and haste" and equip {2}.